Nyssen has been the president of the Belgian Association of Geomorphologists from 2017 through 2021,[2] and was editor-in-chief of the Land Degradation and Development journal from 2019 to 2020.[3]
Nyssen co-edited the book Geo-trekking in Ethiopia's Tropical Mountains: The Dogu'a Tembien District and self-published a book in the Tigrinya language.[1][4]
Nyssen's research showed that high levels of soil loss in the Ethiopian highlands are caused by a combination of erosive rainfall, steep slopes, and impacts of deforestation, overgrazing, an agricultural system where the open-field system dominates, and the aftermath of poverty induced by a long history of feudalism in Ethiopia. He further studied how the high density of soil and water conservation structures led to land resilience in the highlands.[5]
Through the use of rephotography, Nyssen linked changes in the landscape with land degradation.[6]
Nyssen notes that Ethiopian farmers have ploughed the same lands and hills for thousands of years with oxen ploughs. They know their soils and know when rains will come or what they have to plant if rains are late.[7][8] Since his first stay in Ethiopia in 1994, Nyssen observed that the amount of food available to rural households, as well as the overall living standard has strongly improved.[5][9]
Nyssen's research in Belgium is also related to the consequences of human activities on geomorphic processes: the reintroduction of beavers, spoil tips of the derelict coal mining industry, and the age-old agriculture in the Pays de Herve region, which led to the occurrence of lynchets or cultivation terraces, by analogy to a common practice in current Ethiopia;[10]
The beaver dams have drawn his attention because they contribute to conserving water in the rivers' headwaters. He studied their effect on discharges of the Chevral creek, that is part of the Ourthe basin. The research confirmed that such dams have a buffering effect on discharges: downstream the peak discharges are much lower than what was observed before beaver reintroduction.[11]
When war erupted in Tigray in 2020, Nyssen advocated strongly for a ceasefire and humanitarian aid for the people of Tigray,[12][13] and helped expose starvation and extreme civilian sufferings in Tigray.[14][15]
^ abNyssen, Jan; Frankl, Amaury; Zenebe, Amanuel; Deckers, Jozef; Poesen, Jean (October 2015). "Land Management in the Northern Ethiopian Highlands: Local and Global Perspectives; Past, Present and Future". Land Degradation & Development. 26 (7): 759–764. doi:10.1002/ldr.2336. S2CID129501591.
^Nyssen, J.; Naudts, J.; De Geyndt, K.; Haile, Mitiku; Poesen, J.; Moeyersons, J.; Deckers, J. (May 2008). "Soils and land use in the Tigray highlands (Northern Ethiopia)". Land Degradation & Development. 19 (3): 257–274. doi:10.1002/ldr.840. S2CID128492271.
^Nyssen, J.; Pontzeele, J.; Billi, P. (May 2011). "Effect of beaver dams on the hydrology of small mountain streams: Example from the Chevral in the Ourthe Orientale basin, Ardennes, Belgium". Journal of Hydrology. 402 (1–2): 92–102. Bibcode:2011JHyd..402...92N. doi:10.1016/j.jhydrol.2011.03.008.
